Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.93   12.578%   $64.0907   $64.09   $64.10   $64.10  
  Purchase #2 $68.39   8.547%   $74.2353   $74.24   $74.25   $74.20  
  Purchase #3 $112.26   9.418%   $122.8326   $122.83   $122.85   $122.80  
  Purchase #4 $196.77   4.241%   $205.115   $205.12   $205.10   $205.10  
  Purchase #5 $65.25   6.846%   $69.717   $69.72   $69.70   $69.70  
  Purchase #6 $116.84   7.735%   $125.8776   $125.88   $125.90   $125.90  
  Purchase #7 $108.70   13.616%   $123.5006   $123.50   $123.50   $123.50  
  7 purchase totals = $725.14       $785.3688   $785.38   $785.40   $785.30